Symplast vs. Apoplast Water Transport in Plants

Steps:

• Define symplast pathway: water moves cell-to-cell via cytoplasm and plasmodesmata, excluding intercellular spaces.
• Define apoplast pathway: water flows through cell walls and intercellular spaces, bypassing plasma membranes and plasmodesmata.
• Evaluate statement 1: false, as symplast avoids intercellular spaces.
• Evaluate statements 2–4: statement 2 false, tonoplast (vacuolar membrane) does not block cell-to-cell symplast movement; statements 3 and 4 true, apoplast excludes plasmodesmata and is blocked by Casparian strip in endodermis.

Why D is correct:

• Statements 3 and 4 match apoplast definition: extracellular flow without plasmodesmata, halted by Casparian strip's impermeable lignin barrier forcing symplastic entry.

Why the others are wrong:

• A includes false statement 1 (symplast uses plasmodesmata, not spaces).
• B includes false statement 1.
• C includes false statement 2 (tonoplast separates vacuole from cytoplasm but doesn't block symplast).

Final answer: D